Buildings are the number one end users of energy. They are responsible for about 40% of all energy consumption and carbon emissions in both developed and developing countries. One of the main reasons behind such huge consumption is that the majority of the existing building stock today is over 20 years old, and thus, most existing buildings have under-performing and inefficient building systems compared to the current technologies. That is why many cities that have recently committed to reducing their greenhouse gas emissions have started to target the energy efficiency of the existing building stock with measures that address all building systems, particularly those associated with and influenced by the building envelope.
The significance of the building envelope comes from the fact that its thermal performance and weather tightness determine the amount of energy needed to maintain a comfortable indoor environment relative to the outdoors. In fact, building envelope components can significantly impact heating, cooling, and ventilation loads in addition to lighting, which are the main areas of energy consumption in building operations. For example, it is estimated that about one third of the energy consumed in commercial buildings for heating and cooling is associated with windows.
Taking that into consideration, several research reports have highlighted that 20-40% of the total energy savings in buildings is projected to be from windows and building envelopes. This is because up until the 1980s, windows, curtain walls, and skylights were mainly single-glazed with frameworks that had no thermal breaks. These inefficient glazing systems result in significant heat loss in the winter and heat gain in the summer, and thus, lead to higher energy consumption for heating and cooling to maintain a comfortable indoor environment.
Today, it is estimated that about 40% of all commercial and multi-family residential buildings in the United States, for example, still have single-pane windows, and about half of the remaining 60% have early or low-performing double-pane window systems that lack significantly in performance compared to the current technologies and building and energy code requirements. The problem is that replacing these inefficient glazing systems with new, high-performing ones is often not a feasible option for most buildings due to the associated complexity, high upfront costs, building and business disruption, and long payback periods.
Additionally, most glazing systems, including the current ones, are still being designed with little consideration (if any) given to the high possibility of them requiring a retrofit in the future, leaving building owners with limited options when the need arises. That is why most façade and window retrofit practices available today include intrusive and complex measures that are associated with high upfront costs, building and business disruption, and long payback periods as well, and thus, they are often not considered a feasible option for most buildings.
Therefore, there is a growing technical and environmental need for feasible glazing and window retrofit solutions that can be widely adopted by most existing buildings to improve their energy efficiency.